Can we save item in list through infopath and save the item as form in document library. Means the data should be saved at both the places simultaneously(list/library) on a button click without using any add on.
You need code to write the fields of an InfoPath browser form into a SharePoint list. There is a 3rd party code library from Qdabra called QRules that has that code, and more. It costs less than a day's development time.
If you do not want code or any external tools, you could promote the desired form fields as columns in the forms library. That way you have both: a document library for the forms, and the columns in the library to report on the form data.
Edit: You can select the columns to promote when you first publish the form to a forms library.
If the form and the library already exist, you can change the Form Options under the File tab.
Select Property Promotion, click the Add and Remove buttons to control which fields will be promoted. You can use the Modify button to use different column names from the form field names. Click OK and publish the form again.